Co掺杂SnO_2纳米粉的微结构和磁学性质

采用湿化学方法制备了Co掺杂的二氧化锡纳米粉(Sn1-xCoxO2),经研究发现,Co以离子形式存在,而不是以单质形式存在,样品中除了金红石型的SnO2相之外,没有发现其他杂质的相,随着Co掺杂含量的增加,晶粒尺寸减小,光吸收谱红移,禁带宽度线性下降。钴离子磁矩随掺杂含量的增加而减小,这可能是由于占据晶格上近邻阳离子位置的磁性离子数目增加使磁性离子成反铁磁性排列的结果。     

Echoes of Veblen's theory of business enterprise in the later development of macroeconomics: Fisher's debt-deflation theory of great depressions and the financial instability theories of minsky and tobin

Irving Fisher's debt-deflation theory of great depressions, first published in 1932 and 1933, was invoked by Hyman Minsky and James Tobin as a crucial precursor of their theories of macroeconomic financial instability. This paper argues that Wesley Mitchell was right to perceive a close intellectual affinity between Fisher's debt-deflation theory and Thorstein Veblen's Theory of Business Enterprise (1904), and that this affinity also exists between Veblen (1904) and the analyses of Minsky and Tobin.     

Beyond Miami: The Ethnic Enclave and Personal Income in Various Cuban Communities in the United States1

It is frequently noted that Cubans living in Miami are successful because they benefit from the formation of an enclave economy. Using the 1990 Census Public Use Microdata, this study broadens the examination beyond Miami to address the question of why Cubans living elsewhere have higher earnings than those in Miami. Specifically, I address the question of whether there is a relationship between Cuban ethnic enclave participation and Cuban income. Findings indicate that Cubans in Miami have the lowest personal income. Cubans living in areas with the lowest Cuban populations have the highest incomes. These findings are evidence against the enclave economy hypothesis.     

Immigrants' Language Skills: The Australian Experience in a Longitudinal Survey

This article is concerned with the determinants of English language proficiency (speaking, reading and writing) among immigrants. It presents a model of immigrant destination language proficiency based on economic incentives, exposure to the destination language, and efficiency in second language acquisition. A unique data set, the Longitudinal Survey of Immigrants to Australia, is used to test the model. This survey had three waves, at about six months, eighteen months and three‐and‐a‐half years after immigration. The analyses are performed by wave, type of language skill and gender using probit analysis. Bivariate probit analysis is used across waves. The hypotheses are supported by the data. The bivariate probit analysis indicates a positive correlation in the unexplained component that declines with time between waves, suggesting a “regression to the mean” in the unobserved components of English language proficiency.     

Sociology and the Second Darwinian Revolution: A Metatheoretical Analysis

Sociologists tend to eschew biological explanations of human social behavior. Accordingly, when evolutionary biologists began to apply neo‐Darwinian theory to the study of human social behavior, the reactions of sociologists typically ranged from indifference to overt hostility. Since the mid‐1960s, however, neo‐Darwinian evolutionary theory has stimulated a "second Darwinian revolution" in traditional social scientific conceptions of human nature and social behavior, even while most sociologists remain largely uninformed about neo‐Darwinian theory and research. This article traces sociology's long‐standing isolation from the life sciences, especially evolutionary biology, to divergence in the metatheoretical assumptions that typify conventional sociological thought versus contemporary evolutionary biology. We conclude with a discussion of the recent emergence of a nascent "evolutionary sociology" that integrates sociobiological reasoning with contemporary sociological thought.     

Horticultural Decline in the Vale of Evesham,U.K., 1950–1980

There has been little geographical research on the spatial decline of particular agricultural enterprises. This paper traces the regression of horticulture in the Vale of Evesham since 1950 and shows how spatially the decline has been from the periphery inwards, leaving a distinct ‘core’ of production to the east of Evesham. Reasons for the demise of horticulture, both internal and external to the Vale, are outlined and it is demonstrated how the present plight of this part of the Avon Valley is the result of a complex interplay of economic, social, institutional and physical factors.     

ON SELECTING VARIABLES AND ASSESSING THEIR PERFORMANCE IN LINEAR DISCRIMINANT ANALYSIS

Linear discriminant analysis between two populations is considered in this paper. Error rate is reviewed as a criterion for selection of variables, and a stepwise procedure is outlined that selects variables on the basis of empirical estimates of error. Problems with assessment of the selected variables are highlighted. A leave-one-out method is proposed for estimating the true error rate of the selected variables, or alternatively of the selection procedure itself. Monte Carlo simulations, of multivariate binary as well as multivariate normal data, demonstrate the feasibility of the proposed method and indicate its much greater accuracy relative to that of other available methods.     

U.S. Aviation Regulations Increase Probability of Midair Collisions

A purely stochastic Monte Carlo model is used to compare the relative midair collision course probabilities and mean closing velocities of four systems of rules for aircraft cruising altitudes as a function of altitude error: (1) current U.S. federal rules, (2) random altitudes, and (3) two proposed alternatives to the current rules. This model increments error while: (1) counting collisions among cruising pairs of aircraft following the four rules being tested on random headings between randomly placed airports, and (2) calculating mean closing velocities for each rule. The calculations verify that: (1) federal rules increase collision course probabilities by about four times more than for a chaotic system of aircraft cruising at randomly selected altitudes, (2) risk is directly proportional to the level of compliance, and (3) mean closing velocities resulting from the current rule are slightly less than for random altitudes, while being almost twice as high as for the proposed rules. High closing velocities are shown to increase the collision probability.     

Public Opposition to a Proposed Nuclear Waste Repository in Canada: An Investigation of Cultural and Economic Effects

Residents of four northern communities were surveyed about Atomic Energy of Canada Limited's proposal to site an underground repository for high-level nuclear waste somewhere in the Canadian Shield. Opposition to the repository was relatively strong in all communities, but was strongest among aboriginal respondents. Path analysis revealed that trust in nuclear regulators, faith in science and technology, and anticipated net costs were important mediators of this effect. Aboriginals were less trusting, exhibited less faith in science and technology, and perceived the costs associated with the repository to be higher than their nonaboriginal counterparts. No support was found for the hypothesis that, after controlling for aboriginal status, financially insecure individuals would display greater support for the nuclear waste repository than financially secure individuals. Policy implications for balancing perceived risks and siting needs are discussed.